In a letter to Republican senators made public on Thursday, the
GAO said the Defense Department broke the law by not notifying
the appropriate congressional committees of the swap at least 30
days in advance of the exchange. A section of the 2014 Department
of Defense Appropriations Act prohibits the department from using
appropriated funds to transfer Guantanamo Bay detainees without
notifying Congress at least 30 days in advance.

The GAO also said the Pentagon violated the Antideficiency Act —
which prohibits federal
agencies from spending money in excess of the amount available in
appropriated funds — since no funds were technically available to
transfer the detainees. The government spent almost $1 million to
transfer the detainees, according to an email sent from the
Pentagon to the GAO.

"In our view, DOD has dismissed
the significance of the express language enacted" in the
appropriations act, GAO counsel Susan A. Poling said in the
letter.

The GAO said the relevant
congressional committees weren't notified until the day of the
transfer. Written notification from the Pentagon actually came
two days after the swap.

A senior defense official told
Business Insider the Pentagon disagrees with the GAO's
conclusion.

"The Administration,
after consultation with the Department of Justice, concluded that
the transfer could lawfully proceed in the exercise of the
President’s constitutional authority. GAO expressly does not
address the lawfulness of the Administration’s actions as a
matter of constitutional law," the official said.

"The Administration had a fleeting opportunity to protect
the life of a U.S. service member held captive and in danger for
almost five years. Under these exceptional circumstances, the
Administration determined that it was necessary and appropriate
to forego 30 days’ notice of the transfer in order to obtain SGT
Bergdahl’s safe return."

Pentagon spokesman Rear Adm.
John Kirby later defiantly said the operation was "conducted
lawfully."

Caitlin
Hayden, a spokesperson for the White House's National Security
Council, said in June that the administration determined the
30-day requirement did not apply in these unusual circumstances.
She said Secretary of Defense Chuck Hagel, acting on behalf of
the president, determined the normal notification process could
endanger Bergdahl's life.

"In these
circumstances, delaying the transfer in order to provide the
30-day notice would interfere with the Executive’s performance of
two related functions that the Constitution assigns to the
President: protecting the lives of Americans abroad and
protecting U.S. soldiers," Hayden said.

"Because such
interference would significantly alter the balance between
Congress and the President, and could even raise constitutional
concerns, we believe it is fair to conclude that Congress did not
intend that the Administration would be barred from taking the
action it did in these circumstances."